In an integrated search system, an integrated search server issues a cross search request to a plurality of search servers, and outputs an integrated search result in which search results obtained from the respective search servers have been integrated. Since the integrated search system uses the plurality of search servers, a simple cross search request and a simple process for integrating the search results may cause inconvenience. In order to solve this inconvenience, a method of exchanging information other than the search request and the search results between the integrated search server and the search servers, and realizing an optimal integrated search system is required.
For example, a score of a document in the search result which has been calculated by each search server may change depending on contents of an index included in the search server. In this case, since respective documents in the integrated search result in which the search results obtained from the respective search servers have been integrated have the scores calculated from different perspectives, a sequence of the documents in order of score in the integrated search result is not appropriate. In order to overcome this problem, there is an approach in which the integrated search server exchanges statistical information for scoring, with each search server, and thereby, a score value after the integration is calculated in each search server (for example, see Patent Literature 1). In this approach, first, when the integrated search server issues the search request to each search server, each search server transmits statistical information which has been created based on an intermediate result obtained by a search operation, to the integrated search server. Next, the integrated search server aggregates each statistical information, creates global statistical information, and transmits the global statistical information to each search server. Lastly, each search server calculates the score based on the global statistical information, and transmits the search result to the integrated search server. According to this approach, optimal scoring can be performed for the entire integrated search system.